HER2 protein is a member of the human epidermal growth factor receptor family. There are four members of this family which are plasma membrane bound receptor tyrosine kinases. Breast cancer is the most prevalent cancer in women, and about 25% of cases show HER2 gene amplification. Breast cancers with HER2 gene amplification or HER2 protein overexpression are typically referred to as HER2-positive in pathology reports. HER2-positive breast cancers tend to grow faster and are more likely to spread and recur compared to HER2-negative breast cancers. HER2 amplification is a major therapeutic target in breast cancer. There are medicines specifically for HER2-positive breast cancers. Lapatinib, which is an orally active drug approved for breast cancer treatment, is a dual tyrosine kinase inhibitor which targets both HER1 and HER2 tyrosine kinase activity. Two therapeutic antibodies, including Trastuzumab and Pertuzumab, targeting HER2 receptor are also approved by the FDA for breast cancer patients.
Cancer evolution and progression are driven by a sequence of somatic genetic and nongenetic alterations resulting in more favorable tumor cell growth and survival. Cancer genetic evolution is subject to intrinsic influences such as the tumor microenvironment, as well as extrinsic pressures such as drug therapy. The clinical pattern of acquired resistance may, in many circumstances, represent outgrowth of resistant clones, which may have originally been present in the cancer at low frequency as a result of intratumoral genetic heterogeneity, but grow out under the selective pressure of targeted therapy.
Advances in high-throughput sequencing technologies are beginning to establish a molecular taxonomy for a spectrum of human disease and have facilitated a move toward precision medicine. With regard to oncology, defining the mutational landscape of a patient's tumor will lead to more precise treatment and management of individuals with cancer. In addition to the potential for identifying ‘actionable’ therapeutic targets in cancer patients, the clinical sequencing may also shed light on acquired resistance mechanisms developed against targeted therapies. Although uncovering the DNA sequences of tumors becomes possible with the advances in next generation of sequencing (“NGS”), this technology does not provide any functional information of the identified mutations. Therefore, there is a need to develop a novel method to study the functional consequence of mutation(s) on the target gene activity and its response toward the drug treatment. This functional information will provide additional valuable guidelines for the physician to choose the most appropriate treatment based on the mutational landscape of a patient's tumor.
Accordingly, there is a continuing need to develop an improved clinical test using a cell-based assay that measures HER2 activity useful in assessing the effect of somatic HER2 gene mutations in the respective protein activity, as well as determining the sensitivity of HER2 variants to inhibitors.